Telomere Maintenance in Cancer Cell Division

Steps:

• Telomeres are repetitive DNA sequences at chromosome ends that protect against degradation.
• During DNA replication (S phase), normal cells face the end-replication problem, shortening telomeres.
• Cancer cells activate telomerase, a reverse transcriptase enzyme that adds telomeric repeats to counteract shortening.
• In mitosis (M phase), chromosomes with maintained telomeres are equally distributed to daughter cells without length change.

Why D is correct:

• Telomerase in cancer cells elongates telomeres during replication, ensuring daughter cells receive chromosomes of the same telomere length per the enzyme's definition as a ribonucleoprotein that synthesizes TTAGGG repeats.

Why the others are wrong:

• A: Length typically stays stable, not increases, unless telomerase activity exceeds normal compensation.
• B: Shortening occurs in normal somatic cells, not telomerase-active cancer cells.
• C: Complete loss would cause chromosomal instability and cell death, which cancer cells avoid through maintenance.

Final answer: D